Reload 275G TSX for AR

[msd4141]

Hello everyone,
I am hoping to get some help on reloading the 275G TSX for the bushmaster in AR platform. I loaded a dummy round with a new, sized starline brass and crimped in the last groove which gave me a COL of 2.32 inches. This is to tight to fit in My AR magazines as the AR is designed for 2.26 inch max length( although it barely fits in one of my magazines) How are people loading this for the AR? I have H110, W296, and LiL Gun powders. I have been loading the 250G FTX and the Barnes 200G XPB bullet using Hoots load data (Thanks Hoot for your postings on the 200G XPB) I read about the Barnes 275 TSX and wanted to experiment with that load so I bought a few boxes. Do you load to a coal of 2.26 with that bullet and not crimp in the groove? Seems like that would reduce the bullet case capacity which may raise the pressure in the case. Thanks for any insight to this, Marc

[MOOSE EARS]

As always, your loads need to be developed with your rifle. I am loading 40gr of LilGun with the bullet seated and crimped in the upper cannelure. The length is a perfect fit in the mag and chambers flawlessly. Be warned, this is a HOT load and should only be attempted if worked up and pressure signs are kept in check. These rounds cloverleaf at 100yds, if I hold still! Stay safe!

[Bmt85]

Most AR mags won't load past 2.30ish. You have to window your mag. Basically cut a slit wide enough in the front of the mag to fit the nose of the bullet without hitting the sides of the opening. Also, cut the opening low enough to fit as many rounds as you want.

Here's a pic from Cavity Back bullets who offers modified 223 mags from time to time.
https://www.cavitybackbullets.com/product-p/cb-pri-mod-5.56.htm

I load the 275 TSX around the same (mine is actually around 2.33-2.34"), taper crimp and stab crimp. I also use Lilgun. One of my rifles can run 40 or 41gr, with Lilgun, one my others will only go to 38gr. So yeah, Start low and work up. Also, IMO, Lilgun is a little fast for the 275 TSX. It works, but it's on the edge. Will still probably beat Win296, even though Win296 is a little slower. You could try something a little slower than Win296, but faster than 1680.

[msd4141]

I may try to window a mag. The bushmaster AR mags I have are metal, and I have a dremel. I have heard H110 is basically the same as W296, Is this statement accurate? I Reload for several calibers, and always start low when first working up a load, so I want to and will be safe. I looked around for a barnes load data sheet, could not find one. I have 3 loading books, none from barnes though. I will be using rem 7 1/2 primers for this load. BMT, you say you load yours out to 2.33 to 2.34" do you use that load in an AR? 2.30 to 2.32 is the length I want to use so I can crimp in the cannelure. I do not have a tool to measure the bullet is in the lands. I tested my dummy round which is 2.32" and the bolt closed just fine on my AR

[Bmt85]

Windowing a mag isn’t hard with a dremel.

From everything I’ve read, h110 is the same as w296.

Search the forum, I’m pretty sure one member emailed Barnes and got some load data from them. If I had to guess, loading long and using h110, starting load will probably be around 35-36 gr, but I don’t know for sure.

I do use the 275 TSX in my AR’s. I have only used Lilgun, so far anyway. When I load around 2.33” OAL, that lets me taper crimp just inside the driving band (cannelure).

You really should get an OAL gauge, but most bullets will load without hitting the lands in the 450B. For my barrels, and others I have read about, the 275 TSX won’t hit the lands until 2.42” or so. So you should be good, but I can’t guarantee it.

[msd4141]

Thanks for the replies. I will continue to research the topic. You are right, I should invest in a gauge, just most of my reloads are for pistols which head space off of the casing mouth. Thanks again, Marc

[msd4141]

I have succesfully windowed a mag to accept the 275G TSX. I will load to Case length of 2.32 to 2.34 and crimp in the cannelure. I will be using REM 7 1/2 primers. I have LiL Gun and H110 and I want to try both to see which has better accuracy. I will be testing in my AR with a tromix 18" barrel. I will start low and work up in .5 grain increments. Does anyone have suggestions on where to start with each Powder? I still can not find Barnes or Hodgen info when loading for an AR. I see BMT85 says start with 35,or 36 grains H110, How about with LiL gun? Thanks

[Al in Mi]

Hogdon online data has it, the TSX data is the same Barnes sent me.

[Al in Mi]